1. Field of the Invention
Embodiments of the present invention relate in general to footwear, and particularly to energy absorption and return systems for use in athletic footwear.
2. Related Art
In prior U.S. Pat. Nos. 5,437,110 and 5,596,819, issued in the names of two of the inventors herein, a discussion was provided of the desirability of providing adjustable foot-strike energy shock absorption and return. Those patents disclosed the use of a device disposed in the midsole of a shoe under the heel. The device used an adjustable mechanism to store and return to the wearer's foot shock energy experienced during walking or running.
Those prior patents discussed a variety of related art, including U.S. Pat. Nos. 4,486,964, 4,506,460, 2,357,281, 2,394,281, 4,709,489, 4,815,221, 4,854,057, and 4,878,300 as disclosing a variety of spring systems for shoes that related to heel-strike energy absorption and return. Since the time of those patents, other patents and applications have addressed a variety of spring mechanisms for shoes. See, e.g., U.S. Pat. Nos. 6,282,814, 6,751,891, 6,865,824, 6,886,274, 7,159,338, 7,219,447, 7,287,340, and 7,290,354, as well as published applications 2005/0166422 and 2009/0064536.
A step forward or stride consists of a dynamic process sometimes referred to as gait. The science surrounding gait is extensive but embodiments of the present invention focus upon that aspect that a layman might identify as toe-off when jumping. Gait can be broken down into three distinct phases as follows: (1) the contact phase which begins with heel strike and continues until the foot is flat on the surface, (2) the mid-stance phase beginning from the foot flat and a shift of body weight and continuing until the heel rises, and, lastly, (3) the propulsion phase where toe-off (or jumping) would occur.
The related art does not focus upon the propulsion phase of the gait cycle. Most of the devices are directed to the contact phase and use heel-related mechanisms to store and return energy. Because energy stored in the contact phase via a heel spring is dissipated by the time the propulsion phase begins, heel springs have not proven effective for energy storage and return. Some of the related art also use springs under the ball of the foot. In addition to not being effective in the propulsion phase, such devices can have adverse physiological effects on the foot if not properly positioned.